1. Field of the Invention
The present invention relates to motor drive circuits and electronics and particularly to motor drive circuits capable of driving motors regardless of a difference between input modes in type and electronics equipped therewith.
2. Description of the Background Art
Stepping motors characteristically have an angle of rotation varying in proportion to the number of pulses input. Conventionally, how a stepping motor should be rotated has been controlled by controlling a current passing through the stepping motor.
For example Japanese Patent Laying-open No. 8-149892 discloses a stepping motor drive device receiving a signal indicating in which direction a stepping motor should rotate and a pulse signal to drive the stepping motor. This drive device operates in accordance with the stepping motor's drive mode to vary a pattern of a current passing through a stator of the motor. If the drive device switches a current pattern between a first current pattern and a second current pattern the drive device switches the current pattern such that the motor generates the same torque.
Another example is a stepping motor drive device disclosed in Japanese Patent Laying-open No. 8-037799. When this drive device switches an excitation mode from a first excitation mode to a second excitation mode the drive device does so after the motor has completely shifted from a first step to a second step.
Note that a stepping motor has an excitation mode including W1-2 phase excitation, 1-2 phase excitation, 2 phase excitation, and the like. W1-2 phase excitation is an excitation mode allowing an exciting current to be controlled to render an angle of rotation per step smaller than a fundamental step angle. It is also referred to as “microstep driving.” The angle of rotation of W1-2 phase excitation per step is ½ of that of 1-2 phase excitation and ¼ of that of 2 phase excitation. Accordingly, 2 phase excitation, 1-2 phase excitation and W1-2 phase excitation are also referred to as full step excitation, half step excitation and quarter step excitation, respectively.
In most cases, stepping motor drive circuits utilize a current chopper circuit capable of controlling an output current to be constant. For example if a stepping motor is driven in a W1-2 phase excitation mode the current chopper circuit receives a control signal, which is divided mainly in two types (or input modes, as will be referred to hereinafter). These two types of input modes will hereinafter be referred to as a “clock input mode” and a “parallel input mode”.
FIG. 13 is a diagram for illustrating how the clock input mode and the parallel input mode are distinguished.
With reference to FIG. 13, a drive circuit 101 drives a motor M, which is a stepping motor. For the clock input mode, drive circuit 101 receives four types of signals CLK, CW_CCW, and MODE0 and MODE1. Signal CLK is a clock signal. Whenever signal CLK rises (or falls) drive circuit 101 rotates motor M by a predetermined angle. Signal CW_CCW is a signal controlling in which direction (i.e., clockwise or counterclockwise as seen with respect to the axis of rotation) motor M should rotate. Signals MODE0 and MODE1 are signals that determine the stepping motor's excitation modes (or predetermined angles, as aforementioned).
For the parallel input mode, drive circuit 101 receives six types of signals PH1 and PH2, and I01, I11, I02 and I12. Signals PH1 and PH2 indicate which polarity an exciting current that passes through the stepping motor has. Signal I01, I11, I02, I12 indicate an exciting current in amount. Signals PH1, and I01 and I11 in combination indicate an exciting current of one phase in polarity and amount (or level). Signals PH2, and I02 and I12 in combination indicate an exciting current of another phase in polarity and amount (or level).
As shown in FIG. 13, the clock input mode and the parallel input mode employ significantly different types of control signals, respectively. As such, if a stepping motor and its drive circuit are mounted in some equipment, one of the two types of drive circuits must be selected. Which one of the two types of drive circuits is selected is determined by the specification of the equipment.
For example if the input mode of the drive circuit mounted in the equipment is the clock input mode, it is difficult to replace the drive circuit with that of the parallel input mode, since the equipment would be significantly changed in design. This can be an obstacle for example in selling drive circuits of the parallel input mode. While herein a drive circuit of the parallel input mode has been described by way of example, that of the clock input mode is also similarly discussed. Solving such problem requires a designer to develop two types of drive circuits. This, however, imposes an increased burden on the designer.